This invention relates to control of a motor/generator provided with a plurality of independently rotating rotors and one stator.
Tokkai-Hei-8-340663 published by the Japanese Patent Office in 1996 discloses an electric motor provided with a plurality of independently rotating rotors and a single stator.
This motor comprises two groups of coils on the stator designated for each rotor so that two rotors rotate separately.
Two inverters are provided in order to control the electrical current applied to each group of the designated coils.
Since the above electrical motor uses two groups of coils and two inverters, large current loss inevitably results.
In this context, U.S. Pat. No. 6,049,152 discloses a motor/generator in which two rotors having magnets with different numbers of poles are rotated independently by applying a composite current to a single group of stator coils from a single energizing circuit.
However a demagnetization effect occurs when the poles of the magnets facing each other are identical. As a result, when the motor/generator is continuously used at high temperatures, the possibility arises of deterioration in magnetic properties due the demagnetization effect.
It is therefore an object of this invention to protect the magnet from suffering magnetic deterioration by controlling the energizing current of the stator coils.
In order to achieve the above object, this invention provides a current control device for such a motor/generator that has a stator provided with a plurality of coils, a first rotor provided with a fixed number of magnetic poles facing the stator, and a second rotor provided with fewer magnetic poles than the first rotor. The magnetic poles of the second rotor also face the stator.
The control device comprises an inverter which regulates a wave form of an AC power current flowing through the coils in response to a signal, and a microprocessor. The microprocessor is programmed to calculate a wave form of a first current flowing through the coils which generates a rotating magnetic field which is synchronous with a magnetic field produced by the first rotor, calculate a wave form of a second current flowing through the coils which generates a rotating magnetic field which is synchronous with a magnetic field produced by the second rotor, calculate a wave form of a correcting current which, at a position where a specific magnetic pole in the first rotor and a pole of the second rotor with the same polarity face each other, increases a density of a magnetic flux passing through the specific magnetic pole, and generate the signal which realizes a composite wave form comprising a wave form of the first current, a wave form of the second current and a wave form of the correcting current.
This invention also provides a control method for such a motor/generator that has a stator provided with a plurality of coils, a first rotor provided with a fixed number of magnetic poles facing the stator, and a second rotor provided with fewer magnetic poles than the first rotor. The magnetic poles of the second rotor also face the stator.
The control method comprises calculating a wave form of a first current flowing through the coils which generates a rotating magnetic field which is synchronous with a magnetic field produced by the first rotor, calculating a wave form of a second current flowing through the coils which generates a rotating magnetic field which is synchronous with a magnetic field produced by the second rotor, calculating a wave form of a correcting current which, at a position where a specific magnetic pole in the first rotor and a pole of the second rotor with the same polarity face each other, increases a density of a magnetic flux passing through the specific magnetic pole; and providing the coils with a power current of a composite wave form comprising a wave form of the first current, a wave form of the second current and a wave form of the correcting current.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.